Why your conservatory is too hot, too cold, and hard to sell

I owned a house with a conservatory. Over a year I used it for perhaps a month, maybe two at the outside, as a sitting room. The rest of the year it was a room I walked past.

That is not unusual, and it is worth being precise about how usual it is. I have been inside more than twenty houses with conservatories. The number that were comfortable to sit in across a full year, without someone having already replaced the roof and put radiators in, is none.

The reason it is cold is the reason it was cheap

A conservatory usually avoids building regulations approval, and that exemption is most of why one costs what it costs. The conditions attached to it are worth reading slowly, because they are usually presented as technicalities and they are actually a description of the room you are buying.

It has to be at ground level. It has to be under thirty square metres. It has to be separated from the house by external-quality doors or windows. And it has to have its own independent heating.

Read that last pair again. To qualify, the room must be sealed off from your house by what is effectively an external door, and it must not be on your heating system. Those are not incidental hurdles. They are the building regulations describing, accurately, a structure that sits outside your home rather than inside it, and treating it accordingly.

So when people say a conservatory is a cheap way to add a room, they have it slightly wrong. It is cheap because, officially, it is not a room in your house.

What that means in July and January

The roof does the rest. Almost every one I see is around fifteen years old with a polycarbonate roof, and they are nearly all the same. In July it is too hot to breathe in there. In January it is cold enough that you shut the door and forget about it.

What owners actually do with the space follows from that. Plants, mostly, and whatever needs putting somewhere. Plenty of people furnish them properly, with chairs and a table, and then hardly ever sit in them. People do try to heat them. A radiator helps, an electric heater helps less, and both are working against a roof designed to let heat straight through in both directions.

The radiator deserves a moment on its own, because of where it leaves the exemption. Independent heating was one of the four conditions, and a radiator fed off the house's central heating is not independent heating. An electric heater standing in the corner is, which puts the cheaper and less effective option on the safer side of the line. If you are thinking about plumbing a radiator in, ask where that leaves you before the work happens, rather than finding out when a buyer's solicitor asks.

The second sale

There is a whole industry fitting solid and tiled roofs to conservatories that already exist, and I want to be fair to it, because the product is good. They look very stylish, and the room usually does become usable afterwards.

Two things to know before spending the money.

The first is that the roof is not the only way heat leaves. If the windows are old, the room will still be cold in winter with a beautiful new roof on top of it, and you will have solved half a problem at full price.

The second is that replacing the roof requires building regulations approval. That follows from everything above: a solid roof takes the structure out of the exemption it was built under, which means the thing you are creating is no longer a conservatory in the regulations' eyes.

Cost depends on size and on which roof you choose. A flat roof is the cheaper route and starts somewhere around £8,000. Tiled costs more.

The arithmetic nobody lays out

Put those two purchases next to each other and look at the order they happen in.

You buy a glazed room, priced low because the regulations treat it as separate from your house. You discover that it is separate from your house. You then pay again, with building control involved this time, to make it part of your house.

Add the two together and you are into the money a modest extension would have cost, having arrived there backwards. Which is why the right choice comes down to budget and personal preference, and why if you can afford an extension, a conservatory is never the right answer. Ranked, it is a proper extension first, an orangery second, a conservatory third.

Notice what is missing from that answer. It has nothing to do with what sort of house you own. A conservatory works or fails on how it is built and on what you decide to do about heating and cooling, and almost nothing else.

What buyers actually do about it

Here is the part that surprises owners most. Buyers are not shocked by your conservatory. They can see it in the photographs, they knew it was there before they made an offer, and how conservatories are is common knowledge by now.

They also do not tell you what they think of it. Standing in one, most of them are quietly working out what they would turn it into.

The discount arrives later, and it arrives through the survey. Once that comes back with problems in the foundations, the windows and the doors, the buyer has something specific to point at, and they push. Agents have been quoted saying a conservatory can take as much as fifteen thousand pounds off a house, and from what I have seen that is believable, for a simple reason: it is an unusable room that still has to be maintained.

Almost nobody takes one down before selling. It is a lot of work, and sellers would rather hand over the discount than do it.

It does still count as a room on the listing. It is listed as a conservatory, which tells any buyer reading it exactly what to expect.

The footings, which is where the survey problems start

Old conservatories and orangeries are frequently built on footings that are not the same quality or depth as a proper extension's, and damp and moisture problems follow. I see it most in orangeries, which carry more masonry.

This is the same fault line running through everything above. The structure was built to a standard that suited a room officially outside your house, and it behaves like one for as long as it stands.

The garden it eats

A typical conservatory is around four metres by three, and it takes exactly that much garden. Some are considerably bigger.

Fifteen years ago that trade seemed obviously worth making. It is less obvious now, because what people want from a garden has changed. A good seating area, proper outdoor lighting, somewhere to cook, maybe a pergola. Four metres by three is a generous outdoor room, and a conservatory sits precisely on top of it.

If you have just bought a house with one

Extend, if the budget is there.

If it is not, replace the roof and replace some of the glass, and make a decent job of it. That is genuinely worth doing when you do not want to extend, you would like the room to feel like part of the house, and the windows and structure are not too far gone. That is the case for it, and it is the one I chose: I had a tiled roof fitted and the ceiling plasterboarded from the inside.

Expect the whole thing to start looking dated again after eight to ten years, and expect that number to depend almost entirely on how well it was built the first time. Seals go. Polycarbonate stains and yellows. Leaks appear. None of that is a surprise to anybody who has owned one, and it is why the maintenance nobody mentions at the point of sale is simply the windows and the roof, over and over.